1. Field
Disclosed herein is a method for producing a thermoelectric object for a thermoelectric conversion device, in particular a method for producing a thermoelectric object from a half-Heusler alloy.
2. Description of Related Art
Thermoelectric conversion devices use the Seebeck effect for obtaining electrical energy from heat which is typically wasted. A requisite for the wider use of the thermoelectric effect to convert heat into electric energy is the availability of efficient thermoelectric materials.
The efficiency of a thermoelectric material is described by its ZT value, which is defined by ZT=TS2σ/κ: wherein T is the absolute temperature, S the Seebeck effect, σ the electric conductivity and κ the thermal conductivity. Half-Heusler alloys are considered to be a class of materials with a promising potential for high ZT values. U.S. Pat. No. 7,745,720 B2, for example, discloses half-Heusler alloys for thermoelectric conversion devices.
Half-Heusler alloys represent intermetallic compounds of the general formula XYZ with an ordered cubic C1 b crystal structure. Each of the transition metals X, Y and a main group metal Z occupy one of three nested face-centred cubic (fcc) sublattices. A fourth fcc sublattice is unoccupied. If the sum of the valence electrons in this structure is 18, the compound exhibits a semi-conducting behaviour.
Half-Heusler alloys based on the systems XNiSn and XCoSb (X=Zr, Hf, Ti) are of interest for thermoelectric applications, because they have a high Seebeck effect and a high electrical conductivity. They have, however, relatively high thermal conductivity values as well, so that the ZT value of purely ternary compounds is limited.
In order to increase the ZT value of the half-Heusler alloys, their properties can be modified in a controlled manner by substitutions on all three sublattices. An example for this is the alloy TiNiSn, in which thermal conductivity can be reduced and electric conductivity can be increased by substituting the Ti location by Hf and Zr and the Sn location by Sb.
In order to provide thermoelectric objects for thermoelectric conversion devices which can be implemented in practice, suitable production methods are desirable.